The disclosure relates generally to the field of optical waveguides, such as polymer waveguides. In particular, it concerns an optical waveguide having light-reflecting features such as micro-mirrors.
Optical waveguides, such as polymer optical waveguides, wherein channels are designed to confine and guide an optical signal, are known in the art. Such waveguides may, for instance, be used in the field of optical interconnects, where polymer channels are integrated in layers of printed circuit boards (PCBs). In these interconnects, data are carried by optical signals guided by the polymer waveguide channels.
The confinement of the light in the polymer waveguide channel is known to arise due to a difference between the refractive indices of the channel core and the cladding material, the latter having the lower refractive index. For PCB applications, the polymer waveguide channels may be produced using polymer layer deposition techniques and UV-light exposure for the waveguide core patterning.
In general, the layer-based manufacturing technique used naturally restricts the waveguide routing to a single plane. Even though several waveguide planes can be stacked, they cannot easily be optically connected. Furthermore, the optical properties of the polymer waveguides, e.g., the small refractive index difference between the waveguide core and cladding, require large bending radii of the waveguide channels to avoid excess bending losses. The resulting area demand causes complications for certain routing schemes.
In this respect and for the sake of exemplification, US 2006/0204176 discloses methods for optical routing, which rely on mirrors. As another example, EP 1 715 368 suggests using optical elements, e.g. mirrors, which are positioned within the optical layer during their fabrication process.
A number of papers are further devoted to the subject, such as for example:
“Laser Ablation and Laser Direct Writing as Enabling Technologies for the Definition of Micro-Optical Elements” Nina Hendrickx, Proc. of SPIE Vol. 5956 59561B-5. Here, micro-mirrors are defined as a “hole,” by laser ablation, in the optical layer such as to provide out-of-plane coupling. The mirror effect is obtained due to internal reflection that occurs at the polymer-air interface.
“Chip-to-chip optical interconnects” Kash, J. A, Optical Fiber Communication Conference, 2006 and the 2006 National Fiber Optic Engineers Conference. OFC 2006, ISBN: 1-55752-803-9.
“Fabrication and Characterisation of Direct Laser-Written Multimode Polymer Waveguides with Out-of-Plane Turning Mirrors” A. McCarthy, CLEO05.
“Fabrication of multimode polymer waveguides with integrated micro-mirrors using Deep Lithography with Protons” J. Van Erps, Proceedings Symposium IEEE/LEOS Benelux Chapter, 2004, Ghent.
In addition, another major challenge is the integration of optical, optoelectronic (VCSEL, photodiode) or optomechanical (connector) elements with polymer waveguides. Precise alignment in the range of micrometers is required to maximize the optical power coupled between the optical waveguide and the other element. For example, “active” alignment methods are known wherein, after positioning an element, the optical power is monitored and the position of the element is adjusted until optimum optical power is achieved.
In contrast, “passive” methods are also known, which merely involve a single placement step, whereby an element automatically homes close to an optimum position. Such a method is, for instance, described in U.S. Pat. No. 7,382,954 and U.S. Pat. No. 7,389,015. These approaches make use of specific structures in a metal layer (e.g., copper layer) of a PCB board.
Other methods are described in, for example:
U.S. Pat. No. 7,212,698 (passive alignment method);
Lamprecht, et al., “Passive Alignment of Optical Elements in a Printed Circuit Board”, Proceedings ECTC'06, pp. 761-767;
Dangel, et al., “Polymer-Waveguide-Based Board-Level Optical Interconnect Technology for Datacom Applications”, invited paper in EPEP/SPI (Electrical Performance of Electronic Packaging/Signal Propagation on Interconnects) Special Section of IEEE Transactions on Advanced Packaging, November 2008.